The present invention relates to aerial lift platform apparatus having an extensible boom.
Aerial platform apparatus having an extensible boom have become widely used during the past decade. This apparatus has a chassis which typically is supported by four wheels, two of which are steerable and two of which are driven by hydraulic motors, either forwardly or in reverse. The chassis rotatably supports an upper works, which may rotate about a vertical axis, being driven by a motor designated as a swing motor. The upper works includes an internal combustion engine and a pump, and has supports for pivotally supporting a boom for luffing movement about a horizontal axis. Luffing is controlled by a lift cylinder. The boom is extended and retracted by a boom cylinder. At its outer end, the boom supports a workman's platform, there being a horizontal pivot adjacent the free end of the boom about which the workman's platform can rotate, primarily to maintain the platform level, and there may also be provided a vertical pivot about which the platform may rotate, so that the platform may be positioned towards either side of the boom. A master cylinder senses the elevation of the boom, and transmits fluid to a slave cylinder, which serves to maintain the platform level. An override provision is made, so that the platform may be tilted, as desired. This conventional construction is provided with controls accessible to the workman in the platform, and these controls have included, in the past, chassis controls for driving and steering the chassis, and have included upper works controls, for swinging the upper works, for luffing the boom, for extending and retracting the boom, and for causing rotation of the platform about the horizontal and vertical axes adjacent the free end of the boom.
In the past, the controls for the various movements of the chassis and of the upper works were positioned primarily with a view towards convenience, and possibly economy of construction. Such controls were not optimum from the human factors point of view for convenience of operation and reliability of anticipated operator response. In this regard. workmen are trained in the operation of the aerial work platform apparatus, these workmen are primarily skilled in other duties, such as painting, reconditioning of equipment, maintenance of equipment and installation of various kinds of equipment and apparatus. While training is given to these workmen in the operation of the aerial work platform apparatus, it is usually an adjunct to their primary work tasks, and therefore may not be completely mastered by a workman, or, where there is a person with relatively little experience in the operation of the aerial work platform apparatus, there is a risk that improper movement of the apparatus may occur, due to a workman being confused, or unfamiliar with the result which will be achieved by the manipulation of a particular control member in a particular manner. This occurs, also, where the workman is in a stress situation, is unduly tired, or is otherwise not as alert as he should be. As a result, a movement is caused which is not actually desired, which could possible lead to either damage to the equipment or injury to the workman, or both. For example, if a drive comand is intended, to move the vehicle in a particular direction, and instead the upper works is swung, an injury or damage could result.
Johnston, U.S. Pat. No. 4,160,492 discloses such an apparatus having a control panel on which levers are provided which combine two different functions, depending upon whether they are moved along a first path, or a second path at right angles to the first path. For example, one lever controls both propel movement of the vehicle, and upper works swinging, while another lever combines boom luffing and vehicle steering.
Slusher, U.S. Pat. No. 3,379,279 discloses a three wheel aerial lift platform apparatus having some movements manually controlled and boom luffing controlled by a foot pedal.
Michelson, U.S. Pat. No. 3,424,271 discloses a three wheel apparatus in which control levers are used to effect both driving and steering, and a foot control is provided to effect raising and lowering of a carriage which supports the workman.
There are also known in the prior art control arrangements for a boom lift mounted on a truck. See, for example, Stevenson U.S. Pat. No. 4,044,856 which has controls with rotary motion, and without any relationship to the motion of the workman's platform resulting from operation of a control, and Hall U.S. Pat. No. 3,572,467 which has a horizontally extending lever, movable about a horizontal axis, for controlling boom telescoping movement.
The control systems and arrangements of the prior art are deficient in not providing a clear separation of control member movements and functions, and in not providing a correspondence of control member movements with movement of the apparatus or the part thereof which is moved as a result of the movement of the control member.